As discussed in International (PCT) Publication No. WO 2009/048863, a light guide made of a flexible transparent film sheet can be formed wherein an edge of the sheet is cut or otherwise formed into parallel strips, with the strips then being folded/bent into a stacked array (generally shaped like an elongated beam) through which light can be directed to or from the major area of the sheet (i.e., the portion from which the strips extend). Similar arrangements are seen in U.S. Pat. No. 4,151,582 to Grunberger and U.S. Pat. No. 4,824,194 to Karasawa. So long as the bends of the strips are not too great (which can disrupt the internal reflection that promotes light transmission within the strips), and/or so long as the bent regions are coated to deter light loss at the bends, illumination of the end of the beam-like stack of strips (as with one or more LEDs) transmits light through the strips and into the major area of the sheet. The major area of the sheet can be treated to emit the light from all or a portion of the major area. Such an arrangement is useful for applications such as general illumination, illuminated signage, and backlighting and/or frontlighting of Liquid Crystal Displays (LCDs) or other displays. Conversely, light may be collected in the major area of the sheet and transmitted therein to the beam-like stack for reception by a photovoltaic or other device, which can be useful for applications such as light sensors and solar collectors. Thus, a point or concentrated light source (at the stacked strips) can be used to illuminate a large area (the major area of the sheet), or conversely light incident over a large area (at the major area of the sheet) can be concentrated into a small area (at the stacked strips). Such film light guides have significant advantages over light guides formed of rigid transparent plates or the like owing to their lower cost, size, and weight, and their increased flexibility.
Despite the foregoing advantages, illuminators of the foregoing types are rarely used, largely owing to difficulties with their manufacture. Accurate formation of the strips in the film sheet is accomplished easily enough, as by running an array of blades along a film sheet to an edge. However, it is then difficult and time consuming to properly bend and align the strips into a stacked array suitable for receiving light from a light source. If the bending is done by hand, it is time- and labor-intensive, and if done by machine, it is capital-intensive insofar as it is expensive and difficult to build folding machines which precisely bend the fingers without damage (particularly if the machine is to accommodate sheets of different sizes with different strip configurations). It would therefore be useful to have more efficient and economical devices and methods for constructing film illumination devices such as those described in the foregoing patents.